Adhesives, often referred to as cements, glues or pastes are defined generally as substances capable of holding materials together by surface attachment. Adhesives may attach to surfaces and develop the internal or cohesive strength necessary to hold the materials together while curing from liquid to solid state, while losing solvent, or during a chemical reaction. Many of the substances designated as adhesives may also be designated as caulking, potting, sealing, casting or encapsulating compounds when employed in a thick mass. In a more restrictive sense, to be termed an adhesive, a substance should be a liquid or a tacky semi-solid, at least for a short period of time to contact and wet a surface, and be used in a relatively thin layer to form a useful joint capable of transmitting stresses from one substrate to another. Thus, the term "adhesives", as used in this specification and in the claims includes cements, glues and pastes.
Solvent cementing is a process in which thermoplastics, usually amorphous, are softened by the application of a suitable solvent or mixture of solvents, and then pressed together to effect a bond. The resin itself, after evaporation of the solvent, acts as the filler. Many thermoplastic substrates are easier to join effectively by solvent cements than by conventional adhesive bonding. Generally, a small amount of the resin to be cemented is dissolved in a solvent to form the cement. The inclusion of the resin aids in gap filling, accelerates setting, and reduces shrinkage and internal stresses.
Solvent cements also have been utilized to bond different plastic materials to each other, but in such instances, the solvent must be a solvent for both plastics. Usually in such instances, a mixture of solvents is used. The solvent softens (dissolves) the surface of the substrate to be bonded, and the surface becomes tacky. At this point, the surfaces are brought into contact with each other, often under pressure, and dried.
For the past twenty-five years, solvent cements have been used for joining ABS (acrylonitrile-butadiene-styrene resin), PVC (polyvinylchloride), and CPVC (chlorinated polyvinylchloride) plastic pipe and fittings. The amount of such plastic pipe used for conveying a variety of liquids is enormous. The major uses are drain, waste, vent, sewer and potable water. Plastic pipe has continued to displace the more traditional materials used for the same purpose such as copper, steel, galvanized metal, cast iron, lead and concrete asbestos pipe. Plastic pipe currently is the material of choice in the home, municipal, and manufacturing industries.
Currently available solvent cements generally have a volatile organic chemicals (VOC, calculated in accordance with ASTM D-2369) of from about 600 to about 850 gms/liter. As a result of this awareness, regulations are being enacted into law by Congress and in the various states for controlling and setting limits for the VOC of paints, coatings and other materials such as solvent cements.
Plastic pipe products including solvent cements, cleaners and primers have now come under newly proposed state regulations. In California, for example, where the first air pollution control regulations were implemented, the California Environmental Quality Act (CEQA) along with the South Coast Air Quality Management District (SCAQMD) and the Bay Area Quality Management District (BAAQMD) have stated that the VOC content of solvent cements must be dramatically reduced by Jan. 1, 1994. Thus, solvent cements as currently formulated for joining plastic pipe cannot be used after Jan. 1, 1993, and unless new solvent cements can be developed which meet the new standards, the use of plastic pipe will become obsolete.
Historically, ASTM specifications were developed and adopted by pipe manufacturers in the early 1970's. Joining materials such as solvent cements were also included, and ASTM specifications were written specifically for these materials. National code organizations such as Uniform Plumbing Code (UPC) and the International Association of Plumbing and Mechanical Officials (IAPMO) adopted ASTM standards which were further adopted and included into state and local plumbing codes for the home, building and construction industries.
In the mid 1970's a third party certification organization, the National Sanitation Foundation International (NSF) became the recognized authority for testing, certifying and listing those manufacturers who voluntarily submit their products to NSF. ASTM tests that apply to plastic pipe products are performed by NSF. The listing book published by the NSF entitles plastic pipe product manufacturers to use the NSF logo or seal on their products. Many local, state and other code bodies have written into their plumbing ordinances that plastic pipe products must bear the NSF seal.
The current ASTM standard which relates to ABS solvent cements is ASTM D-2235 which specifies that the ABS solvent cements will contain a minimum of 15% by weight of ABS resin and the remainder is methyl ethyl ketone (MEK) solvent. To have a useful product, the ABS cement typically utilizes 30% to 35% resin and the remainder is MEK. The purpose of using higher than minimum resin is to produce a product that has a suitable viscosity for application to pipes and fittings. Viscosity is measured in centipoise, and a typical ABS cement will have a viscosity of 1000 to 3000 centipoise.
The ASTM standard for PVC solvent cements is ASTM D-2564. According to this standard, such solvent cements contain a minimum of 10% PVC resin, inert fillers, and the remainder is one or more solvents such as tetrahydrofuran (THF), cyclohexanone (CYH), MEK, and acetone.
ASTM F-493 sets forth the requirements for CPVC solvent cements as containing a minimum of 10% CPVC resin, inert fillers, and the remainder is one or more solvents including THF, CYH, MEK and/or acetone.
All three classes of solvent cement have a high solvent to solids content which is believed to be necessary for a solvent cement to perform satisfactorily. The high solvent content allows for penetration and softening of the pipe outer surface and the surface of the inside of the coupling. Prior to application of the cement, cleaners and/or primers are recommended per ASTM D-2855. Most codes require the use of a cleaner or primer. Rapid evaporation of the solvents is necessary to insure handling strength of freshly solvent cemented pipe and also insuring the final cure. Cure is defined as the stage where most of the solvents applied have evaporated leaving the solvent welded joints fused together so that pressure can be successfully applied.
The need for safer and lower VOC solvent cements which are easy to apply, cost effective, and which cure within a reasonable period of time without the use of heat, pressure, UV light or extraordinary mechanical devices is paramount. The bonding or adhesive properties of the solvent cements must be satisfactory for the intended use whether non-pressure drain, waste or vent (DWV) or pressure systems used in potable water applications.
U.S. Pat. No. 4,687,798 describes and claims a solvent cement for joining polymers comprising from about 10% to 15% of a water-insoluble polymer such as PVC or ABS, and a solvent comprised of ethyl acetate and N-methyl-2-pyrrolidone. The solvent cement may contain a thixotropic agent such as silica. U.S. Pat. No. 4,788,002 claims a similar solvent cement which consists of a solution of a solvent of ethyl acetate and N-methyl-2-pyrrolidone wherein the ethyl acetate ranges from about 3% to about 90% with the balance being N-methyl-2-pyrrolidone.
U.S. Pat. No. 4,098,719 describes polyvinyl chloride solvent weld primer compositions for use in the assembly of polyvinyl chloride pipe and fittings to themselves or to ABS pipe or fittings. The primer consists essentially of an organic solvent containing from about 0.5 to about 2.5 weight percent of an unplasticized polyvinyl chloride resin dissolved in the solvent which is a mixture of tetrahydrofuran and dimethylformamide in a weight ratio of from about 1.64:1 to 1:1.
Solvent cements are also described in U.S. Pat. No. 3,765,983 which are applied with specially-designed applicators. The solvent cements which are described comprise a solution of a PVC, ABS or CPVC in a suitable solvent such as tetrahydrofuran, cyclohexanone, dimethylformamide, or mixtures thereof. The resin in the cement is preferably the same as the resin of the pipe and fittings to be joined.
U.S. Pat. No. 3,770,547 relates to a method for adhesively bonding surfaces which includes the use of adhesives including solvent cements such as volatile solvent solutions of polyvinylchloride, ABS polymers, cellulose acetate, etc., in organic liquid vehicles such as ethanol, methanol, methyl ethyl ketone, acetone, tetrahydrofuran, etc.
U.S. Pat. No. 4,980,383 describes foamable compositions useful in preparing foamed articles. The foamable compositions comprise a chlorinated vinyl resin containing inorganic materials including fibrous materials, a chemical blowing agent and a solvent. The term CPVC is defined in the patent (Col. 5) as including mixtures of chlorinated polyvinyl chloride resin and other resins such as vinyl chloride resin, chlorinated polyethylene, methacrylate-acrylate copolymer, etc.
U.S. Pat. Nos. 3,230,184; 3,873,475; and 4,053,448 relate to polyester resin compositions which contain hollow glass microspheres. The compositions described in the '475 patent are useful as lightweight patching, caulking or sealing compositions, and the '448 patent describes the compositions as being useful patching compositions for repairing imperfections in metal surfaces. The polyester resin molding compositions described in the '184 patent are reported to yield products of substantial strength and lighter weight. The compositions also contain a fibrous filler material in addition to the hollow spheres.
Inorganic filler materials which comprise a mixture of an inorganic powder and inorganic hollow microspheres are reported to be useful in a curable polyester composition in U.S. Pat. No. 5,028,456. The curable composition comprises, in addition to the inorganic filler, at least one unsaturated polyester resin, at least one hydrocarbon monomer copolymerizable with the polyester, and at least one aryl sulfonamide-aldehyde resin. The compositions are useful as plastic body fillers for repairing metal surfaces.
U.S. Pat. No. 5,252,634 describes low volatile organic compounds emitting thermoplastic pipe adhesives which include at least one resin such as PVC, CPVC and acrylics, or ABS, a solvent blend, a low specific gravity filler such as hollow ceramic microspheres, and a thixotropic agent (e.g., silica) for maintaining the homogeneity of the adhesive mixture.